Display apparatus and assembly of its driving circuit

ABSTRACT

A display apparatus and an assembly of a driving circuit for the display apparatus having a display device, a film carrier with a lead to transfer a signal for driving the display device, and a bus board to supply a signal to the lead. A dummy lead is provided along the outside of each of an input side outer lead and an output side outer lead of the film carrier. A predetermined voltage is applied to the dummy leads. The predetermined voltage value is set to a value so as not to stationarily cause a DC bias for the voltage of the outer lead on the outside.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a display apparatus which is used for atelevision receiver, a view finder of a video camera, a light bulb of avideo projector, a display of a computer, or the like and, moreparticularly, to an assembly of a driving circuit of such a displayapparatus.

[0003] 2. Related Background Art

[0004] As a recent display apparatus, attention is paid to a displayapparatus having a display device such as liquid crystal device, plasmalight emitting device, electrochromic device, electron emitting device,or the like in place of a CRT.

[0005] Each of those display devices has a number of pixels and has anelectrode to apply an electric signal to decide an optical state of eachpixel.

[0006] Further, in order to apply the electric signal to the electrodeof the display device, a rigid wiring board called a bus board or adriver board and made of glass epoxy or the like and a flexible wiringboard such as a TAB film or the like are used.

[0007] Such a structure has been disclosed in U.S. Pat. No. 5,019,201 or5,360,943 or the like.

[0008] A case where a liquid crystal display panel is used as a displaydevice and a film carrier having a driving IC chip is used as a flexiblewiring board will now be described hereinbelow.

[0009] Hitherto, in case of connecting the film carrier on which adriving circuit is mounted to a display panel and a bus board, there isa drawback such that outer leads locating at both ends among the outerleads on the input side and output side are likely to be damaged by astress from the outside due to a shock, a vibration, a thermal stress,or the like.

[0010] To solve such a drawback, therefore, as shown in FIG. 6, dummyleads 8 and 9 which are electrically not related to the driving for animage display are arranged on both outsides of outer leads 6 and 5 onthe input side and output side among the leads of the film carrier,thereby preventing a damage of the outer leads at both ends due to anexternal stress. In FIG. 6, reference numeral 1 denotes a display panel;2 a driving circuit such as an IC chip or the like; 3 a bus board; 4 afilm carrier; and 7 a soldering land for the dummy leads.

[0011] There is a case where a quality of an image which is displayed ina display area is improved by always holding the outside of the displayarea to display the image to either one of a white state (bright state)and a black state (dark state). Such a method is called a frame driving.

[0012]FIG. 7 shows an example of a display apparatus. Four electrodes 99for a frame driving are provided for the display panel 1 and areconnected to leads for a frame driving of film carriers 4 and 4′arranged at both ends of two bus boards 3. Reference numerals 201 and201′ denote scanning line driving circuits of the film carriers 4 and4′.

[0013] One of methods for the frame driving is a method whereby filmcarriers and driving circuits of substantially the same construction areused as all of the film carriers 4 and 4′ and all of the drivingcircuits 201 and 201′ and the apparatus is driven so as to supply asignal for always holding the pixels (frame pixels) on the electrodes 99for the frame driving in a white or black state to the electrodes 99.

[0014] Another method is a method invented by the present inventors etal., namely, a method whereby the structure of the film carriers 4′ atboth ends of the bus board 3 is made different from a structure of theother film carriers 4.

[0015]FIG. 8 shows a structure of the film carrier 4′ which is used insuch another method.

[0016] It is also possible to construct in a manner such that an inputside and an output side of dummy leads 8′ and 9′ are electricallyshort-circuited and connected in order to supply a signal for, forexample, always displaying in white to the frame driving electrodes 99on the outside of a display area of the display panel 1, the input sideis connected to the bus board 3, and the output side is connected to theterminal of the frame driving electrodes of the display apparatus,thereby directly supplying the signal from the bus board 3 to thedisplay apparatus without passing through the driving circuit 201′ anddriving a frame area.

[0017] In case of the above structure, the same IC chip as that ofanother driving circuit 201 can be used as a driving circuit 201′.

[0018] There is no need to give a special construction or specialdriving control for a frame driving to the IC chip.

[0019] In case of a structure shown in FIG. 6, since the dummy lead 9electrically enters a floating state, it functions as a role of anantenna and radiation noises are generated.

[0020] To avoid such a problem, when the dummy leads 8 and 9 areshort-circuited to the adjacent outer lead 5, the dummy leads 8 and 9cannot be used for the frame driving of the display panel 1.

[0021] In the case where, for example, the dummy leads 8 and 9 are heldto a ground and are fixed to a grounding voltage in order to avoid theelectrical floating state, a stationary DC voltage difference occursbetween the dummy leads 8 and 9 and the outer leads 5 and 6 which areadjacent thereto. At this time, particularly, in a connecting portionbetween the display panel 1 and the outer lead 9 on the output side, afailure such as disconnection or the like due to an electric corrosionis likely to be caused.

SUMMARY OF THE INVENTION

[0022] It is an object of the invention to provide a display apparatuswithout an erroneous operation due to noises.

[0023] Another object of the invention is to provide a display apparatushaving an assembly of a driving circuit which can be also applied to adisplay panel which needs a frame driving.

[0024] Still another object of the invention is to provide a displayapparatus in which disconnection is hardly caused due to an electriccorrosion.

[0025] Further another object of the invention is to provide a displayapparatus having an assembly of a driving circuit in which a generalityis high and costs are low.

[0026] The invention is made in consideration of the above circumstancesand there are provided a display apparatus comprising a display device,a driving circuit mounted on a film carrier to drive the display device,and a bus board to supply a power source and a signal to the drivingcircuit and an assembly of a driving circuit of such a displayapparatus, wherein a dummy lead is provided along the outside of each ofan outer lead on the input side and an outer lead on the output side ofthe film carrier, and a predetermined voltage is applied to the dummyleads.

[0027] In this case, the predetermined voltage value which is applied tothe dummy leads is selected to a value such as not to stationarily applya DC bias to the voltage of the outer lead on the output side.

[0028] One end of the dummy lead is connected to a bus board and theother end is connected to the display apparatus.

[0029] According to the invention, by setting the voltage of the dummylead to a value such as not to apply the DC bias as much as possible fora voltage waveform of the outer lead on the output side, the movement ofions in a connecting portion between the outer lead and the displayapparatus can be suppressed and a failure such as a disconnection or thelike due to an electric corrosion can be prevented.

[0030] Since the dummy lead is not in the electrical floating state,there is no fear of radiation noises from the dummy lead.

[0031] On the other hand, since the dummy leads on the input side andthe output side are common, by arbitrarily setting the voltage to beapplied to a land for the dummy lead on the input side, a voltage can bealso directly applied to the display apparatus through the film carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIGS. 1A to 1C are diagrams showing an assembly according to thefirst embodiment of the invention;

[0033]FIG. 2 is a diagram showing voltage waveforms according to thefirst embodiment of the invention;

[0034]FIG. 3 is a diagram showing voltage waveforms according to thesecond embodiment of the invention;

[0035]FIG. 4 is a diagram showing an assembly of the second embodimentof the invention;

[0036]FIG. 5 is a diagram showing a control system of a displayapparatus of the invention;

[0037]FIG. 6 is a diagram showing a conventional assembly;

[0038]FIG. 7 is a diagram showing a conventional display apparatus;

[0039]FIG. 8 is a diagram showing an example of an assembly; and

[0040]FIG. 9 is a diagram showing a comparison of voltage waveforms ofthe display apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041]FIG. 1A is a plan view showing an assembly of a driving circuitaccording to a preferred embodiment of the invention. FIG. 1B is a crosssectional view taken along the line 1B-1B in FIG. 1A. FIG. 1C is a crosssectional view taken along the line 1C-1C in FIG. 1A.

[0042] The structure of FIG. 1A can be used in place of all of the filmcarriers 201 and 201′ in the diagrams.

[0043] Reference numeral 1 denotes the display panel as a displaydevice. The display panel 1 has a number of pixels. Reference numeral 2denotes the IC chip as a driving circuit; 3 the bus board; 4 the filmcarrier; 5 the outer lead on the output side; 6 the outer lead on theinput side; 8 the dummy lead on the input side; 9 the dummy lead on theoutput side; 16 a soldering land as a connecting terminal on the busboard side; 18 a soldering land for the dummy lead; and 15 an electrodeof the display panel. The electrodes 15 are connected as scanningelectrodes or information electrodes to the pixels.

[0044] Reference numeral 19 denotes a dummy lead of the display panel.In case of performing the frame driving, the dummy lead 19 functions asan electrode for the frame driving and is extended into the displaypanel. However, in the other cases, the dummy lead 19 is not extended asshown in FIG. 1A. AD denotes a connecting member such as soldering,anisotropic conductive adhesive agent, or the like.

[0045] The driving circuit 2 applies a voltage necessary for driving thedisplay panel 1 to the display panel 1 through the outer lead 5 on theoutput side. Such a voltage supply is performed on the basis of a powersource and a signal which were supplied from the group of input sideouter leads 6 electrically connected to the bus board 3.

[0046] The voltage that is applied to the display panel 1 through theoutput side outer lead 5 in this instance is shown in FIG. 2.

[0047] In case of using the driving circuit 2 as a circuit for drivingthe scanning electrodes, a waveform A in FIG. 2 is time-sequentiallyoutputted to the driving electrodes 15. In case of using the drivingcircuit 2 as a circuit for driving the information electrodes, awaveform B in FIG. 2 according to an image to be displayed is outputtedto the driving electrodes 15. A reference voltage VC is applied to thedummy electrode 19 of the display panel 1 from the land 18 of the wiringof the bus board without passing through the driving circuit 2.

[0048] When the scanning side waveform shown as a voltage waveformexample A of the outer lead 5 on the output side is seen with respect toonly a period within the period of time shown in FIG. 2, although itsaverage voltage is a plus voltage, a duty of the scanning side waveformis small and is equal to or less than {fraction (1/400)}. Therefore, itcan be regarded as almost zero DC voltage for the reference voltage VCwhen it is seen as a voltage in, for example, one frame period. In theinformation side waveform example shown as a voltage waveform example Bof the output side outer lead, an average voltage value in onehorizontal scanning period is equal to zero for VC.

[0049] The dummy lead 9 on the output side is electrically connected tothe dummy lead 8 on the input side and the dummy lead on the input sideis connected to the land 7 for the dummy lead on the bus board 3 bysoldering, so that the voltage of the output side dummy lead 9 can bearbitrarily set.

[0050] At this time, for example, assuming that the voltage of theoutput side dummy lead 9 is set to VC as shown in FIG. 2, a voltagedifference between the output side dummy lead 9 and the output sideouter lead (in case of an example on the information side) on theoutermost side that is adjacent to the dummy lead 9 is equal to zero asa DC level at least in one horizontal scanning period. An instantaneousvoltage difference is also equal to |V₊−VC| at most, the movement ofions can be suppressed to a low level. Thus, a leading electrodes of thedisplay panel 1 made of a thin metal (for example, aluminum) film havinga thickness within a range from hundreds of Å to thousands of Å can beprotected from a damage due to an electric corrosion.

[0051] A case where, for example, a voltage waveform shown in FIG. 3 isapplied to the output side dummy lead will now be described.

[0052] That is, it is used for applying to the electrodes 99 in what iscalled a frame driving area arranged on the outside of a display area ofthe display panel 1 as shown in FIG. 4 through the dummy lead 9 arrangedon the panel outside of the driver IC 201′ on the outermost side in thegroup of driver ICs 2 mounted on, for instance, a TAB film shown in FIG.7 and for always fixing the frame driving portion to a white display ora black display.

[0053] At this time, an alternating voltage difference whose DCcomponent is equal to zero is caused between the output side dummy lead9 and the output side outer lead (corresponding to the electrode on theinformation side) on the outermost side that is adjacent to the dummylead 9 only for one horizontal scanning period during which the voltagefor the frame driving is applied. For the other period of time in oneframe, even an alternating voltage difference doesn't occur between thedummy lead and the outer lead and the DC component is equal to zero anda DC level is equal to zero. The instantaneous voltage difference isequal to 2|V₊−VC| at most. When it is compared with the case where thevoltage of the output side dummy lead is fixed to VC, although thevoltage difference is larger, its level is almost equal to a voltagedifference between the output side outer leads. The output side dummylead portion is not weak particularly for the electric corrosion.

[0054] In each of embodiments shown in the diagrams, the voltage whichis applied to the dummy electrode of the display panel or the electrodefor the frame driving through the dummy lead has been directly suppliedto the display panel from the bus board through the film carrier withoutpassing through the driver IC. However, a form in which such a voltageis applied through the driver IC can be also used.

[0055] In case of the form of applying the voltage through the driverIC, since the number of terminals of the driver IC increases, the formshown in the diagram is more preferable in an apparatus whichpreferentially intends to realize low costs.

[0056] The driver IC is not necessarily the film carrier package IC butmay be also a driver IC provided as a COG (chip-on-glass) on the displaypanel.

[0057] It is sufficient not to cause a DC component in the voltagedifference between the dummy lead and the lead adjacent thereto for aperiod of time longer than one horizontal scanning period. However, itis preferable that there is no DC component in one horizontal scanningperiod. It is, therefore, sufficient to decide a voltage to be appliedto the dummy lead so as to eliminate the DC component.

[0058] As the number of dummy leads, it is sufficient that at least onedummy lead is provided on each of the right and left sides of the groupof outer leads per one film carrier. More preferably, two to four dummyleads are arranged on each of the left and right sides.

[0059] As a display panel which is used in the invention, a liquidcrystal device, a plasma light emitting device, an electrochromicdevice, an electron emitting device, or the like can be mentioned.Particularly, the invention is effective for a non-active matrix typedevice using a chiral smectic liquid crystal or a chiral nematic liquidcrystal or an active matrix type device using a TN liquid crystal.

[0060] An image display apparatus using the liquid crystal devices inthe embodiments described above will now be explained.

[0061]FIG. 5 is a block diagram of a control system of the image displayapparatus. Reference numeral 200 denotes a display panel in which apolarization plate is combined to the foregoing liquid crystal deviceand which has a back light source as necessary. Reference numeral 201denotes the scanning line driving circuit including a decoder and aswitch; 202 an information line driving circuit including a latchcircuit, a shift register, a switch, and the like; 203 a voltagegenerating circuit for generating a number of reference voltages whichare supplied to both of the driving circuits 201 and 202; 204 a controlcircuit which includes a CPU and an RAM to store image information andoutputs signals to be supplied to the outer lead and the dummy lead; and210 an image signal source such as image sensor for inputting an image,computer which executes an application program, or the like.

[0062] The invention is applied to an assembly with at least any one ofthe display panel 200, scanning line driving circuit 201, andinformation line driving circuit 202.

[0063] As compared with the case where the output side dummy lead 9 isfixed to the GND level as shown in FIG. 9, a fact that the apparatus ofthe invention is strong several times for the electric corrosion hasbeen confirmed by the following reliability tests.

[0064] As for the structure of FIG. 6, a pitch of the output side outerleads (=leading electrode pitch of the display panel) is set to 100 μmand a leading electrode construction is formed by the electrodes inwhich ITO (1000 Å) and aluminum (3000 Å) are laminated on a soda glass.VC is set to 20 V, V₊ is set to 26 V, and V is set to 14 V. Under anenvironment of 45° C./95% RH, the output side dummy lead is fixed to theGND voltage and driven as in the conventional apparatus shown in FIG. 9.In this case, a disconnection due to the electric corrosion occurs inthe leading electrode portion connected to the output side dummy lead 9and in the leading electrode portion adjacent to the above leadingelectrode after the elapse of 168 hours. On the other hand, in the casewhere the output side dummy lead is fixed to the VC voltage and isdriven as shown in FIG. 2, it has been confirmed that no failure due tothe electric corrosion occurs even after the elapse of 1000 hours.

[0065] As described above, according to the invention, the input sidedummy lead and the output side dummy lead of the film carrier on whichthe driving circuit is mounted are commonly constructed and the voltageof the dummy lead is set to be almost zero for the voltage waveform ofthe output side outer lead, so that the movement of ions in theconnecting portion of the outer lead and the display apparatus can besuppressed. The failure such as a disconnection due to the electriccorrosion or the like can be prevented.

[0066] Since the dummy lead is not in the electrical floating state,there is no fear of radiation noises from the dummy lead.

[0067] On the other hand, since the input side dummy lead and the outputside dummy lead are commonly constructed, by arbitrarily setting thevoltage to be applied to the land for the input side dummy lead, thevoltage can be also directly applied to the display panel withoutpassing through the film carrier.

What is claimed is:
 1. An assembly of a driving circuit for a displayapparatus comprising a display device, a film carrier having a lead totransfer a signal for driving said display device, and a bus board forsupplying a signal to said lead, wherein a dummy lead is provided alongthe outside of each of an input side outer lead and an output side outerlead of said film carrier, and a predetermined voltage is applied tosaid dummy leads.
 2. An assembly according to claim 1, wherein saidpredetermined voltage value which is applied to said dummy lead is setto a value that is decided so as not to stationarily cause a DC bias fora voltage of said output side outer lead.
 3. An assembly according toclaim 1, wherein one end of said dummy lead is electrically connected tosaid bus board and the other end is electrically connected to saiddisplay device.
 4. A display apparatus comprising: a display devicehaving a group of electrodes for supplying signals to pixels; a bus fortransferring the signals which are supplied to said group of electrodesor signals to drive said electrodes; and a film carrier having a groupof leads for electrically connecting said group of electrodes of saiddisplay device and connecting terminals of a bus board; wherein saidfilm carrier has dummy leads on both sides of said group of leads, and aDC component of a voltage difference which is caused between said dummylead and a lead adjacent to said dummy lead is almost equal to zero in apredetermined period of time.
 5. An apparatus according to claim 4,wherein voltages (V₊, V⁻) of both polarities for a center voltage (VC)are applied to said group of electrodes, and a voltage of the samepotential as said center voltage is applied to said dummy leads.
 6. Anapparatus according to claim 4, wherein a scanning non-selection voltage(VC) and scanning selection voltages (V₊, V⁻) are applied to said groupof electrodes, and a voltage of the same potential as said scanningnon-selection voltage is applied to said dummy leads.
 7. An apparatusaccording to claim 4, wherein a signal is supplied to said dummy leadsfor a predetermined period of time and said dummy lead is held at apredetermined voltage for a period of time other than said predeterminedperiod of time.
 8. An apparatus according to claim 4, wherein a voltagefor a frame driving is applied to at least one of said dummy leads. 9.An apparatus according to claim 4, wherein said film carrier has adriver IC.
 10. An apparatus according to claim 4, wherein said dummyleads and a dummy electrode of said display device are electricallyconnected.
 11. An apparatus according to claim 4, wherein said dummyleads and a dummy electrode or an electrode for a frame driving of saiddisplay device are adhered by an anisotropic conductive adhesive agent.12. An apparatus according to claim 4, wherein said dummy lead is heldat a predetermined voltage for at least one frame period of time.
 13. Anapparatus according to claim 4, wherein said dummy leads are held at apredetermined voltage for at least one frame period of time.
 14. Anapparatus according to claim 4, wherein said film carrier has an inputside outer lead that is connected to said bus board, an output sideouter lead that is connected to said display device, and a dummy leadfor short-circuiting said bus board and said dummy electrode or saidelectrode for the frame driving of said display device.
 15. Anapparatus-according to claim 14, wherein said input side outer lead andsaid output side outer lead are connected to a driver IC, and said dummylead is not connected to said driver IC.
 16. An apparatus according toclaim 4, wherein said display device is any one of a liquid crystaldevice, a plasma device, an electrochromic device, and an electronemitting device.
 17. An apparatus according to claim 4, wherein saidpredetermined period of time is longer than one horizontal selectionperiod of time.
 18. An apparatus according to claim 4, wherein saidpredetermined period of time is one frame period of time.